Ian Clark's book offers the most comprehensive analysis of legitimacy in international relations available today, in the process breathing new life into the concept of international society. Organized into two main sections—a historical review of major peace settlements and an analysis of contemporary international society—the book develops a framework designed to disentangle the complex threads of discourse that make up both scholarly and public discussions of international legitimacy. The author refines and brings the tradition of the English School into direct dialogue with mainstream U.S. international relations discourse, to productive effect.

Clark treats legitimacy as an irreducibly political concept, subject to historical changes in consensual norms and balances of power. He argues that legitimacy is related, but not reducible to, other norms. Commentators and political actors draw on norms such as justice, rights, or balance of power to give substance to their legitimacy claims, but “legitimacy possesses no independent normative content of its own” (p. 207). International legitimacy is, according to Clark, both a political practice and a property of international society (p. 30). As a practice, it entails negotiation by political actors seeking a working consensus in the context of competing norms and interests. As a property, international legitimacy belongs to international society. International society is constituted by two core sets of legitimacy principles: one set pertaining to who the rightful members are, the other pertaining to how they should conduct themselves. The meaning and content of these core sets of principles vary historically (p. 5).

This variation is skillfully detailed in the historical sections of the book, which cover familiar ground: the Peace of Westphalia, Utrecht, Versailles (where legitimacy proved elusive), and the post–World War II settlement. Clark admirably manages the dual task of synthesizing vast bodies of scholarship on these cases and providing fresh insights based on his analytical framework. For example, he situates the birth of international society, and hence the notion of international legitimacy itself, in the Peace of Westphalia (p. 61). His related argument that Westphalia was not primarily about sovereignty but rather about internationally sanctioned legality is elegantly rendered and might productively mediate the debate about whether or not Westphalia deserves its iconic status in international relations scholarship.

In his treatment of the interplay among norms, interests, and the balance of power in the Vienna Congress, Clark draws on Hans Morgenthau and Paul Schroeder to show how the notion of balance of power was given normative content in the idea of a “just equilibrium.” He thus avoids reducing norms to a distribution of power, and analyzes instead the interplay among power, self-interest, and societal norms, an interplay that makes up the political practice of legitimacy (p. 107). The author deftly avoids reductionism throughout the book, and he never gets bogged down in the rhetoric of constructivist-realist-liberal paradigm wars, though his analysis has much to offer in that vein. The book is free of the methodological self-consciousness characteristic of much IR scholarship in the United States, and adopts instead a pragmatic, interpretive approach disciplined by careful delineation and consistent application of core concepts, and a willingness to systematically engage alternative interpretations of his cases.

In the second half of the book, readers will encounter a broad, nuanced, and open-ended exploration of claims about the meaning and substance of international legitimacy today. Two arguments nested therein will surely invite further debate. With respect to rightful membership, Clark argues that international society has become increasingly stratified and exclusive since the end of the Cold War. This is evident in the robust assertion of liberal democracy as a criterion for membership in the “civilized” society of states, and the simultaneous willingness to categorize certain states (such as Slobodan Milosevic's Yugoslavia, Saddam Hussein's Iraq, and North Korea) as rogues or outlaws. The scope of international society, which has undergone periods of both expansion and contraction since Westphalia, now seems to be contracting (Chapter 9).

Clark leaves us wondering about the status of those states in the world, such as China and Saudi Arabia, that are neither “rogues” nor liberal democracies. Does the fact that international society has not openly deemed these states illegitimate merely represent the dying residue of a once-robust pluralism? He examines armed interventions in the Gulf War of 1991, Kosovo, and the Iraq war of 2003 to demonstrate the increasing willingness of international society to penetrate the internal affairs of states. But these cases could just as easily be taken as the exception rather than the rule, since “failed” states are as often neglected as subject to intervention (though this fact could be used to obliquely support his core argument). A more bothersome oversight is Clark's failure to discuss the pressures for market liberalization that surely constitute a core component of today's model of legitimate statehood, and may be in tension with the pressure to democratize.

U.S. hegemony is another core preoccupation. International society, Clark points out, has historically shown an antihegemonial bias, a commitment to “just equilibrium” rooted in a balance of power. Does the fact of U.S. preponderance undercut the processes of consensus-seeking diplomacy and bargaining that have characterized the workings of international society to date? Is the quest for international legitimacy doomed in the face of unipolarity? Clark has not given up on international society (nor on the United Nations). The problem today, as he sees it, is how to craft consensus on a “just disequilibrium”—a constitutional order based not on balance of power but on U.S. hegemony, constrained by an international society whose members accept the special responsibilities and rights of the hegemon.

Whatever one makes of this less-than-radical conclusion, the notable achievement of this book is to formulate a working conception of international legitimacy and consistently apply it to shed light on both historical cases and contemporary issues. Few international relations scholars today can demonstrate such range and relevance; Legitimacy in International Society will pay substantial dividends to the attentive reader.